Functionally dedicated, morphologically distinct, and stereotypically connected cortical areas are the building blocks of the mammalian cerebral cortex and are essential for its proper function. Nonetheless, the developmental origins of distinct areas are not well understood. The experiments described in this proposal examine the hypothesis that Eph receptor tyrosine kinases and their ligands, the ephrins, define distinct regions of the forming neocortex during development and influence the formation of specific connections between the cortex and thalamus. To test this hypothesis, three specific aims are proposed: 1) Characterize Eph family gene expression in the developing mouse cerebral cortex in the presence and absence of proper patterns of thalamic innervation. These experiments will provide information about what Eph family members are present in the cortex as it becomes parcellated and will address the influences of thalamocortical innervation on these patterns of gene expression. 2) Isolate and characterize transcriptional regulatory regions from cortically expressed genes, obtaining genomic sequences capable of driving cortex-specific gene expression in vivo. Such promoters and enhancers will be invaluable for our studies and will be widely used in the study of the cerebral cortex by others. 3) Generate or maintain lines of mice with perturbed expression of Eph genes within their cerebral cortices and characterize cortical organization and patterns of connections between the cortex and thalamus in these mice. Mice mutant for particular Eph family members are available through collaboration. In addition, we will generate transgenic animals which overexpress particular Eph family members, either spatially or temporally. Changes in the cortices of these mice will be assessed morphologically, molecularly, and connectionally. Thus, this proposal begins to address the role of Eph family members in the parcellation of the neocortex into functional areas, examining potential roles in the formation and maintenance of cellular compartments, as well as in the establishment of proper synaptic connections during cortical development.